In recent years, it has been demanded that the throughput of an interface connecting LSIs to each other be improved, as an LSI clock frequency increases. To improve the throughput of the interface, the rise of the signal frequency per terminal and the increase of the number of terminals are necessary. However, when the number of the terminals is increased, the area of wiring lines occupied in an LSI package increases, and a wiring length required for the connection tends to increase. On the other hand, when the signal frequency per terminal is raised, the attenuation of an electrical signal per unit length increases, and hence a line length is limited. Therefore, even for a high-speed signal having a high frequency, there is required a contrivance such as the employment of a transmission line or the like in which the attenuation is minimized.
It is effective to use an optical transmission line as a transmission line which scarcely affects the signal attenuation dependent on the signal frequency. For example, when an optical fiber is used, the signal attenuation due to the transmission through the fiber having a length of about several ten meters can substantially be ignored. When such an optical transmission line is used, it is advantageous to perform electrical/optical signal conversion at a position very close to the LSI. Therefore, there has been investigated a structure in which an optical interface module having a photoelectric conversion function is arranged very close to the LSI package.
Above all, an LSI package has been proposed in which an interposer (a rewiring substrate) including a signal processing LSI mounted thereon is assembled on a printed wiring board (PWB) by use of a usual mounting step, and then the optical interface module is mounted on the interposer without performing any thermal step later on, whereby the interface module is not thermally influenced (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2004-253456).
However, in the structure disclosed in the above document, there may be a problem that the positioning of the interface module and the interposer is difficult. For this kind of positioning, there is a method in which reference holes and guide pins are used, but in this method, the guide pins need to be inserted into the plurality of reference holes, respectively. Therefore, clearances are required between the reference holes and the guide pins. This reason is that if the diameter of each guide pin is not smaller than that of the reference hole, the guide pins cannot be inserted into the reference holes, even when a slight deviation (pitch deviation) is produced between the reference holes or between the guide pins. Moreover, the clearances include the pitch deviations and the fluctuations or errors of the hole and pin diameters, and hence they become causes to disturb the highly precise positioning. In consequence, there may be a problem that restrictions are placed on a narrow pitch constitution using a large number of pins for the electrical connection between the interface module and the interposer.